Electrodeposition of copper from a cyanide bath



United States Patent Office 3,269,925 Patented August 30, 1966 3,269,925 ELECTRODEPOSITION OF COPPER FROM A CYANIDE BATH Arthur H. Du Rose, Euclid, Ohio, assignor to The Harshaw Chemical Company, Cleveland, Ohio, a corporation of Ohio No Drawing. Filed Jan. 24, 1964, Ser. No. 339,867 17 Claims. (Cl. 20432) This invention relates generally to the addition of certain organic phosphate esters to copper cyanide plating baths and more particularly the invention relates to the addition of phosphate esters of polyoxyethylenated alkylphenols to the baths as wetting agents, agents to conteract the efiect of contamination, and the like. Further, the invention relates to copper cyanide plating baths including the phosphate esters as a constituent there-of.

Of the various electroplating baths for depositing decorative copper plate, the cyanide bath is the most exten sively used, more so than the acid copper baths such as, for example, the sulfate and fluoroborate baths. The cyanide bath has excellent throwing power and approaches 100 percent cathode efficiency. Moreover, copper is plated from the monovalent state in the cyanide bath whereas copper is plated from the divalent state in the acid bath; twice as much copper will be deposited from the cyanide 'bath as from the acid copper baths for any given current density. Another advantage of the cyanide baths over the acid baths is that the yanide bath can be used to plate copper directly on steel and zinc die castings-acid baths require a copper strike.

The copper cyanide plating baths to which the phosphate esters may advantageously be added generally comprise copper cyanide, sufiicient alkali metal cyanide to form the well known water-soluble complex and provide excess alkali metal cyanide, a source of hydroxyl ions and an alkali metal base such as sodium carbonate. The operating pH of the bath is normally adjusted to a value ranging from 11-13 using the hydroxides of lithium, sodium or potassium preferably. Complexing agents such as Rochelle salts, citrates, EDTA ethylenediaminetetraacetic acid) and some gluconates may advantageously be added to the bath to obtain effects well known to those skilled in the art.

Ordinarily, a copper deposit from a copper cyanide plating bath having no wetting agent is smooth, and free from pitting, blotchiness, and manifest porosity. However, when the copper yanide plating baths become contaminated such as, for example, from drag over of emulsion cleaner residue and the like, pitted, dull and blotchy deposits are obtained.

Usually the articles to be plated must be cleaned completely of surface dirt, grit, grease, and other harmful materials found on the surface of said articles. tional plating cycles usually include one or more cleaning baths in advance of the electroplating baths. These cleaning baths in many instances contain emulsion leaners comprising as one phase, organic liquids such as kerosene and the like or a petroleum sulfonate, trieth-anolamine soaps, and the like. After the article has been cleaned, the emulsion cleaner is substantially removed by a subsequent water or steam rinsing step. This step, however, many times fails to remove all of the emulsion cleaner dragged over, and during the mass production of certain articles a copper cyanide plating bath gradually builds up intolerable amounts of contamination; the copper plate or deposit then begins to appear with pits, blotches, manifest porosity and other imperfections.

The expressions blotchiness or blotches as used herein are intended to describe the appearance of a cop- Conven- P-OA where m represents an integer from 0 to l inclusive, n represents an integer ranging from 8 to 30 inclusive, A represents a member selected from the group consisting of hydrogen, and an ion capable of rendering the phosphoric acid ester water soluble, R represents an alkyl group having from 4 to 14 carbon atoms; and R and R represent a member of the group consisting of hydrogen and a lower alkyl group having from 1-3 carbon atoms.

It is quite unexpected that the class of compounds defined by Formula I can be used so effectively in a copper cyanide plating bath to overcome blotchiness, pitting and the like. The identical compounds, when added to a nickel plating bath, fail to improve the nickel deposit and in some instances are even harmful, causing brittle and blotchy deposits. Moreover, classes of phosphate esters other than those defined by Formula I have been found to function variously in copper plating baths. Contrary to the teachings of the prior art, many of the monoand di-phosphate esters of octyl, decyl, dodecyl or octadecyl alcohol, or of hexyl, octyl or dodecyl phenol and their water-soluble salts, as well as the phosphate esters of alkylpolyglycol ethers are not consistently good and are even detrimental in their effect when used in electroplating baths for depositing chromium, nickel, zinc, cadmium, tin, brass, bronze, gold, and silver. It has been found that many of these phosphate esters are extremely harmful, causing imperfections in the resulting metal deposit. Moreover, where the plating baths are strongly oxidizing in character such as the chromium plating baths, the phosphate esters decompose within a few hours.

As indicated hereinbefore the instant invention is carried out by adding small amounts of one or more of the phosphate esters of Formula I, usually in diluted form, to a copper cyanide plating bath. Preferably the ester is added in amounts ranging from about 002 gram per liter to about 0.30 gram per liter. Amounts less than about 0.02 manifest a slight effect in overcoming pitting, blotchiness, and the like, but the improvement may be limited. Ordinarily, the addition of more than 0.3 gram per liter of the phosphate ester is not necessary but excessive amounts cause no harm. The amount of phosphate ester needed to obtain good results is contingent partly on the degree of contamination.

The process of the present invention is particularly advantageous when the electrolysis is carried out using air agitation. Many wetting agents or surfactants commonly used in mechanically agitated or quiescent copper plating baths cannot be used in the identical bath using air agitation because of excessive foaming. This excessive foaming is characterized by a continuous evolution of foam from the bath to such an extent that the bath is rendered practically useless by overflowing of the foam being continuously produced. Certain betaine derivatives or ethoxylated sulfate esters, some of which are the corresponding sulfur analogues of the phosphate esters of Formula I, are effective with the instant copper cyanide baths without air agitation but however cause excessive foaming when used in conjunction with air agitation. Moreover, even with the lower homologues (Where It would represent 5 to 6 or lower) of the compounds defined by Formula I, excessive foaming is still observed. Only the compounds represented by Formula I where n is 8 or above can an acceptable plate of copper be obtained from a contaminated copper cyanide bath without excessive foaming.

The examples of the compounds embraced by Formula I include the monoand di-substituted orthophosphoric acid (H PO esters of polyoxyethylenated alkylphenols and the water-soluble salts thereof including the ammonium salts, the alkali metal salts such as lithium salts, sodium salts, potassium salts and the like, wherein the oxyethylene chain may contain from 8 to 30 ethylene oxide units (C H O); wherein R represents an alkyl radical having from 4 to 14 carbon atoms including those radicals derived from butane, pentane, hexane, etc. through tetradecane and wherein R and R may be hydrogen or a lower alkyl radical having from 1 to 3 carbon atoms including those radicals derived from methane, ethane and propane.

Preferably, however, R is an alkyl radical having 8 to 10 carbon atoms and R and R are hydrogen. There is no preference in using the acid ester as opposed to the salts of the ester. As long as the operating pH (11-13) of the bath is maintained, the free acid ester is shown to be as effective as the water-soluble salts thereof.

Specific ethylene oxide-alkyl phenol reaction products advantageously useful as the monoor di-phosphate ester in carrying the present invention into effect include octaoxyethylenated butylphenol (octaethyleneglycolbutylphenyl ether), nonoxyethylenated amylphenol, decoxyethylenated hexylphenol, undecoxyethylenated heptylphenol, dodecoxyethylenated octylphenol, tridecoxyethylenated nonylphenol, tetradecoxyethylenated nonylphenol, pentadecoxyethylenated nonylphenol, hexadecoxyethylenated nonylphenol, heptadecoxyethylenated decylphenol, octadecoxyethylenated undecylphenol, nonadecoxyethylenated dodecylphenol, eicosoxyethylenated tridecylphenol, pentacosoxyethylenated tetradecylphenol and triancontoxyethylenated nonylphenol. Where the carbon chain exceeds 10 carbon atoms, it is desirable that the ethylene oxide chain contain more than 10 oxyethylene units; usually sufficient solubility is obtained for any of these longer alkyl groups Where the oxyethylene chain comprises 15 units or more.

4 For a class of brighteners particularly useful with these copper cyanide baths see US. Patent 2,862,861. The brighteners disclosed therein are defined by the following general formula:

. the group consisting of methyne A particular phosphate ester which may be used advantageously in carrying out the process of the present invention is the phosphate ester of nonylphenol having an oxyethylene chain comprising 15 (C H O-) units. These particular esters are sold commercially under the trademark Alkapent (M-lS-N representing the monoester and D-lS-N representing the di-ester).

Generally, the phosphate esters of the present invention may be prepared by refluxing an ether solution of an ethoxylated alkylphenol and phosphorus pentoxide. The reactants are preferably kept at a molar ratio of 3 to 1, 3 of the phenol to 1 of phosphorus pentoxide. The conditions for the reaction preferably include reflux at about 36 C. for 12 hours, yielding a mixed product of the monoand di-esters.

The present invention is carried out using any of the copper cyanide plating baths well known to those skilled in the art. Representative of the basic solutions for copper cyanide baths tailored for different purposes are set forth in Metal Finishing Guidebook, Metals and Plastics Publications, Westwoord, New Jersey, 1963, pages 292303.

and nitrogen radicals.

In order that those skilled in the art may better understand how the present invention can be carried into effect the following examples are given by way of illustration and not by way of limitation. All parts and percentages are by weight unless otherwise specified.

The following seven examples were carried out using a bright copper cyanide plating bath having the following:

Components: Grams per liter Copper cyanide (CuCN) 68 Potassium cyanide (free) 18 Potassium hydroxide 20 Thioammeline 1 Potassium carbonate 30 Operating conditions:

pH 12.7 Temp., F. Average cathode current density (ASF) 25 Agitation Air Type current Interrupted current Cycle [sec.(on oif)] 8-2 Example I The above bath is operated at a temperature of about 155 F. and at a current density of 10 to 50 amps. per square foot on a bent cathode, depositing a layer of copper 0.2 to 1.0 mil thick. The resulting copper deposit is smooth, continuous and lustrous being free from pits, blotchiness, porosity and the like. A small amount of an emulsion cleaner compound containing kerosene and rosin soap is added to the bath and another electrodeposit is obtained. This deposit has pits, blotchinesses, and manifest porosity. A small amount (0.05 gram per liter) of Alkapent M-15-N [the mono (nonylphenyl) ester of phosphoric acid having 15 ethylene oxide units] is added to the bath and the electrodeposition of copper is repeated. The resulting copper plate is bright, smooth and continuous and having a quality equivalent to the first copper plate.

Examples Il-VII Repeating the procedure set forth in Example I, Alkapent (M-15-N) is substituted with compounds represented by Formula I wherein (II) m is 1 and n is 8, R is an alkyl group having 9 carbon atoms and R and R are hydrogen; (HI) m is 1 and n is 10, R is an alkyl group having 9 carbon atoms and R and R are hydrogen; (IV) m is 0 and n is 10, and R is an alkyl group having 9 carbon atoms and R and R are hydrogen; (V) m is O and n is 15, R is an alkyl group having 9 carbon atoms and R and R are hydrogen (Alkapent Dl.5-N); (VI) m is 0 and n is 8, R is an alkyl group having 4 carbon atoms and R and R are hydrogen, and (VII) m is 1 and n is 20, R is alkyl group having 14 carbon atoms and R and R are hydrogen. The contaminated baths are made to give deposits equal in quality to the deposits obtained from baths free from contamination.

Comparative Examples VIII-XI Repeating the procedure set forth in Example I, Alkapent M-l5-N is substituted with:

(VIII) The mono-ester of tetraoxyethylenated nonylphenol;

(IX) The di-ester of tet-raoxyethylenated nonylphenol;

(X) The mono-ester of hexaoxyethylenated nonylphenol; and

(XI)The di-ester of hexaoxyethylenated nonylphenol.

The deposits of Examples VIII-X obtained from the contaminated baths containing the esters are considered poor, not discernibly better than the deposits of the baths without the esters. That is, they have surface defects defined above as blotches and the like.

The deposit of Example XI using the contaminated bath containing the ester are considered fair. The deposit is slightly better than the deposit of the bath without the ester but, however, the deposit does not approach the quality of the deposit obtained from the non-contaminated bath.

(XII) Example I is repeated using the same copper plating solution but without the thioammeline brightener. The resulting deposit, even though not bright, is free from blotches and the like,

(XIII) Example IV is repeated but 0.1 gram per liter rhodanine was substituted for the thioammeline. The same results are obtained as in Example IV.

(XIV) Example XIII is repeated using rhodanine as the brightener and the phosphate ester of tetraethyleneglycoln'ionooctylether. The blotchiness caused by the contaminant is not eliminated and foaming is moderate.

(XV) Example I is repeated using the phosphate ester of nonylphenol. The blotchiness is not removed and there is excessive foaming.

(XVI) The phosphate esters as described in all of the previous examples are used also at a concentration of 0.1 gram per liter in grey (Standard Watts Bath) and bright [Watts bath containing 2.5 grams per liter p,p'-oxybis(dibenzenesulfonamide) and .007 gram per liter reduced fuchsin] nickel solutions. In all cases except for the ester used in Example XIV, the ester caused the nickel deposit to be brittle and blotchy.

While specific examples of the invention have been set forth herein above, it is not intended that the invention be limited solely thereto, but to include all of the variations and modifications falling within the scope of the appended claims.

What is claimed:

1. A copper plating bath comprising an aqueous solution of copper cyanide, at least one alkali metal cyanide and an effective amount of at least one compound defined by the following general formula:

where m represents an integer from 0 to 1 inclusive, n represents an integer ranging from 8 to 30 inclusive, A represents a member selected from the group consisting of hydrogen, and an ion capable of rendering the phosphoric acid ester water soluble, R represents an alkyl group having from 4 to 14 carbon atoms, and R and R represent a member selected from the group consisting of hydrogen and a lower alkyl group having from 1 to 3 carbon atoms.

2. The copper plating bath of claim 1 wherein m is 1 and n is 8, R is an alkyl radical having 9 carbon atoms and R and R are hydrogen.

3. The copper plating bath of claim 1 wherein m is 1, n is 10, R is an alkyl radical having 9 carbon atoms and R and R are hydrogen.

4. The copper plating bath of claim 1 wherein m is 0 and n is 10, R is an alkyl radical having 9 carbon atoms and R and R are hydrogen.

5. The copper plating bath of claim 1 wherein m is 1, n is 15, R is an alkyl radical having 9 carbon atoms and R and R are hydrogen.

6. The copper plating bath of claim 1 wherein m is 0, n is 115, R is an alkyl radical having 9 carbon atoms and R and R are hydrogen.

7. In a method of electrodepositing copper on an electroconductive substrate wherein said substrate is subjected to the action of a cleaner in advance of plating said substrate with copper from a bath comprising an aqueous solution of copper cyanide and at least one alkali metal cyanide, the improvement which comprises adding an effective amount of at least one compound defined by the following general formula:

where m represents an integer from 0 to 1 inclusive, n represents an integer ranging from 8 to '30 inclusive, A represents a member selected from the group consisting of hydrogen, and an ion capable of rendering the phosphoric acid ester water soluble, R represents an alkyl group having from 4 to 14 carbon atoms, and R and R represent a member selected from the group consisting of hydrogen and a lower alkyl radical having from 1 to 3 carbon atoms.

8. The method of claim 7 wherein said cleaner is kerosene-containing.

9. The method of claim 7 wherein said cleaner contains a petroleum sulfonate.

10. The method of claim 7 wherein said cleaner contains a triethanolamine soap.

11. The method of claim 7 wherein said cleaner contains a rosin soap.

12. The method of claim 7 wherein said bath is agitated with air.

13. The method of claim 12 wherein m is 1, n is 8, R is an alkyl radical having 9 carbon atoms and R and R are hydrogen.

14-. The method of claim 12 wherein m is 1, n is 10, R is an alkyl radical having 9 carbon atoms and R and R are hydrogen.

15. The method of claim 12 wherein m is 0, n is 10, R is an alkyl radical having 9 carbon atoms and R and R are hydrogen.

16. The method of claim 12 wherein m is 1, n is 15, R is an alkyl radical having 9 carbon atoms and R and R are hydrogen.

17. The method of claim 12 wherein m is O, n is 15, R is an alkyl radical having 9 carbon atoms and R and R are hydrogen.

References Cited by the Examiner UNITED STATES PATENTS 2,853,471 9/1958 Beadell 260-951 XR 3,056,744 10/ L962 Copes et al 260951 XR 3,084,111 4/1963 Strauss et al. 204-52 XR JOHN H. MACK, Primary Examiner.

G. KAPLAN, Assistant Examiner. 

7. IN A METHOD OF ELECTRODEPOSITING COPPER ON AN ELECTROCONDUCTIVE SUBSTRATE WHEREIN SAID SUBSTRATE IS SUBJECTED TO THE ACTION OF A CLEANER IN ADVANCE OF PLATING SAID SUBSTRATE WITH COPPER FROM A BATH COMPRISING AN AQUEOUS SOLUTION OF COPPER CYANIDE AND AT LEAST ONE ALKALI METAL CYANIDE, THE IMPROVEMENT WHICH COMPRISES ADDING AN EFFECTIVE AMOUNT OF AT LEAST ONE COMPOUND DEFINED BY THE FOLLOWING GENERAL FORMULA: 